1. Field of the Invention
The present invention relates to a drive system for a semiconductor laser having a stabilized output.
2. Description of the Prior Art
A forward current versus light output characteristic of a semiconductor laser at room temperature varies depending on process parameters in the manufacture as shown by A(T.sub.0) or B(T.sub.0) in FIG. 1. Only those semiconductor lasers having variations within a permissible range are selected as those which meet specification.
As the surrounding temperature rises above the room temperature, the forward current versus light output characteristic of the semiconductor laser shifts to the right as shown by A(T.sub.1) or B(T.sub.1), and as the temperature falls below the room temperature, the surrounding characteristic shifts to the left as shown by A(T.sub.2) or B(T.sub.2). The amount of shift of the temperature characteristic due to the change of the surrounding temperature depends on the structure of the semiconductor laser.
Further, a forward voltage VF of the semiconductor laser changes with the temperature such that it decreases with the increase of the surrounding temperature.
Such a semiconductor laser has been used in expensive equipment such as a light communication apparatus or a laser beam printer. Such equipment has a strict specification for an input/output characteristic and must be used at a fixed temperature.
Recently, it has been desired to use semiconductor laser in not only the expensive equipment but also inexpensive portable devices such as cameras.
However, the power supply of the inexpensive device such as a camera usually varies in a range of 5-7 volts and is used in circumstances of a large temperature difference such as inside and outside. Accordingly, it has been difficult to use the semiconductor laser in inexpensive portable devices.